hello new kz1000 owner here :D

whats up guys my name is gus...i just purchased a 1977 kz 1000 with 23k on the odo. the bike started fine and went trough all the gears,no some or anything funny,just needs a tune up i guess. the previous owner said he never laid it down, but he is the 3rd owner and hes not sure about the bikes history. since the bike looked all original and had no dents or bent anything i decided to buy it without riding it (inner tube is flat and the battery is dead) i figured for 700 dollars i cant really say no...check it ot here are some pics:

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but as we all know there is a reason why we are all here, to inform or to get information
im tryng to figure out what to do about that inner tube. what size to get and what brand is the most reliable.my tire size is 120/90-18 on the rear. if anyone could please advise me on this, it would be much apreciated. ive googled inner tube size for my tire size and i get a whole bunch of wierd off topic links

welcome!
nice score.
it looks like you have an appreciation for motorcycles from different continents.

leon